First of all, the strict answer to the question “When is a biscotti not a biscotti?” is “never”, because in Italian “biscotti” is a plural word, meaning biscuits, while the singular is “biscotto”. But I think it might sound rather precious in English to say “would you like a biscotto with your tea, Vicar?” Just as it would be to ask for a panino at the sandwich shop, or to munch into an amaretto.
The second problem lies in how English speaking people understand the word biscotti. For many it refers purely to Biscotti di Prato (or Cantuccini), the hard almond slices shown in the picture, and possibly variations on that theme, but not to any old Italian biscuit. However the Italians would be just as happy referring to Amaretti or Custard Creams as biscotti, and if they wanted to refer specifically to Biscotti di Prato they would use the full name.
So what am I to do? Well, I’m going to be brave and talk like the Italians. So when I publish the recipe for Biscotti al Pistacchio, please don’t scream at me if they are just biscuits (though I hope you’ll agree that there’s nothing “just” biscuity about them). I shall be unrepentant in writing about all sorts of biscuits, Italian and otherwise.
Don’t get me started on what the Italians would call the cakes and pastries and loaves that I will also be featuring!